Higher order operators should unsubscribe source promptly #55
Description
WIP.
All higher-order operators should unsubscribe their source immediately on its completion even though it may still be busy with the last inner observable. This is important because the last observable may be of infinite duration, thus blocking cleanup of preceeding source observable. The problem is that when a source blocks on subscribe, the downstream observable will not get a subscription to unsubscribe until too late. Encountered this in .concat_all but there are more of them. Will update with a list of offenders.